"Human-caused climate warming stops when humans stop adding CO₂ to the atmosphere, & emissions of other greenhouse gases are declining sufficiently" (text from @KA_Nicholas)
2. The near-linear relationship between global warming & CO₂ emissions allows a remaining carbon budget to be defined.
This remaining carbon budget can be distributed over time in many different ways, leading to different 'net-zero' years.
3. It is possible to distribute the remaining carbon budget in a way that it never goes below zero (the brown area is the remaining carbon budget).
This is a simplification of reality, but a helpful comparison to other pathways.
4. It may be too difficult or costly to get all CO₂ emissions to zero, & we may instead use Carbon Dioxide Removal (CDR) to offset some of those emissions, such as through modest afforestation.
This means CO₂ emissions go down 𝐬𝐥𝐢𝐠𝐡𝐭𝐥𝐲 slower in the short-term.
5. Nearly all cost-optimising emission scenarios, in contrast, have large-scale CDR. This leads to lower CO₂ reductions in the short-term, large-scale CDR, & a peak & decline temperature profile (overshoot).
CO₂ reductions in the short term are only 𝐬𝐥𝐢𝐠𝐡𝐭𝐥𝐲 lower.
6. These emission profiles have two components:
E) Emissions from sources (e.g., burning fossil fuels)
R) Removals from sinks (e.g., growing a forest)
The "net" is N=E-R, emissions minus removals.
At net-zero, E<R, & since removals are physically constrained, so are emissions.
7. There is a lot of debate on net-zero, but this proposal by @KA_Nicholas gets around the issue (& includes non-CO₂ emissions)
"Human-caused climate warming stops when humans stop adding CO₂ to the atmosphere, & emissions of other greenhouse gases are declining sufficiently"
8. Why do we need CDR in the first place? Well, it may be a more effective way to eliminate all emissions from the 'difficult-to-abate' sectors. science.sciencemag.org/content/360/63…
All tools are needed - efficiency, dematerialisation, technology - CDR wipes up the remaining emissions.
9. There are also non-CO₂ emissions, such as methane from cows & paddy rice, nitrous oxide from fertilisation, air pollutants (causes a 'cooling')
CDR may be needed to offset some warming from non-CO₂, but since most non-CO₂ emissions are short-lived, CDR may not be needed
10. There are many CDR options, but all are limited by scale, in most cases maturity, & in most cases permanence.
Therefore, we should be frugal in their use, & not put all our eggs in the CDR basket.
Sort of obviously, it makes sense to reduce emissions first...
11. Net-zero emissions are the latest rage, but also very confusing:
* Global cost optimal pathways frame the debate
* Net-zero CO₂ & GHG emissions differ
* Loopholes abound
* Ambiguity rules in this space
This question is ambiguous: "How high above pre-industrial levels do you think average global temperature will rise between now and 2100?"
* ...pre-industrial... between "now and 2100"?
* Where we are currently heading or where we could head? This is largely a policy question?
3/
One of the key arguments that Norway uses to continue oil & gas developments, is that under BAU it is expected that oil & gas production will decline in line with <2°C scenarios, even with continued investment.
Let's look closer at these projections & reality...
1/
Here is the projections from the 2003 report from the petroleum agency.
In reality (tweet 1) there was a dip around 2010, but production is now up around 250 million cubic again.
The forecast was totally & utterly WRONG!
2/
In 2011 there was a forecast for an increase in production to 2020, but then a decline. This is probably since they started to put the Johan Sverdrup field on the books.
The increase in production was way too low, again, they got it wrong.
CO2 emissions by fossil fuel:
* We thought coal peaked in 2014. No, & up another 1.1% in 2023
* Oil up 1.5%, on the back of a 28% increase in international aviation & China, but oil remains below 2019 level. 🤞
* Has the golden age of gas come to an end thanks to Russia?
2/
By top emitters:
* China up 4.0% & a peak this year would be a surprise
*US down 3.0%, with coal at 1903 levels
* India up 8.2%, with fossil CO2 clearly above the EU27
* EU27, down 7.4% with drops in all fuels
* Bunkers, up 11.9% due to exploding international aviation
Is the new @DrJamesEHansen et al article an outlier, or rather mainstream?
At least in terms of the key headline numbers, it seems rather mainstream, particularly if you remember most headline key numbers have quite some uncertainty!